The Fink project wants to bring the full world of Unix Open Source software to Darwin and Mac OS X. We modify Unix software so that it compiles and runs on Mac OS X ("port" it) and make it available for download as a coherent distribution. Fink uses Debian tools like dpkg and apt-get to provide powerful binary package management. You can choose whether you want to download precompiled binary packages or build everything from source.

Great solution for a person used to Linux packaging system (Debian in particular) who switched to Mac. I use many more command line tools besides those shipped with Mac OS X and I can't imagine installing and updating those manually - with Fink you can avoid wasting your time on this.

Nice for unix guys like myself who have gotten used to having a huge repository of packages at their fingertips. MacPorts is probably better if you only want to install a few tools, or don't want the fink overhead and don't mind the smaller selection.
I agree on the slow build vs. old package thing, although I usually just go for the old package which runs fine.

Good, but you have to choose between source code taking ages to build, or an outdated binary package. Most of the source builds are also out-of-date in the unstable tree too. Don't get me wrong, it's a very cool package - it's very easy to just grab most of your linux/unix favourites - but it can be outdated. Then again, so are Debian's binary packages sometimes..